The present proposal is designed to determine the extent and to define mechanisms by which prenatal factors constitute predisposition to obesity in children. Longitudinal observations, beginning in fetal life and continuing throughout the fourth year of life are planned in two groups of offspring at high risk for the development of childhood obesity: 1) offspring of normal weight mothers with gestational diabetes. 2) offspring of obese mothers who are non-diabetic. These two groups will be compared with children of non-obese non-gestational diabetic controls. The specific aims are 1) to determine whether maternal insulin resistance in the third trimester of pregnancy predisposes to alterations in fetal and neonatal body composition and neonatal energy expenditure. 2)To determine whether neonatal body composition, energy expenditure or both predict or are determinants of the subsequent development of increased body fat up to three years of age. We intend to thoroughly characterize the in utero environment, and delineate fetal growth rigorously and in detail. We also plan to perform accurate measurements of energy expenditure and body compositions early in life. Over the last year all one year old evaluations have been completed. Data analysis has focused on the antenatal ultrasound and neonatal cord blood and body composition results. This has resulted in the publication of two abstracts and 1 full length paper. Over the next year, 4 year old evaluations will be initiated and data analysis will be performed on neonatal energy expenditure results and one year old body composition and energy expenditure results.